Background. Interferon-gamma (IFN-γ) produced during influenza A virus (IAV) infection stimulates abundant generation of the cytotoxic free radical nitric oxide (NO) in macrophages that in turn damage pulmonary cells and tissues. However, it is unknown whether IFN-γ contributes to the cytotoxicity in the IAV-infected macrophages through the stimulation of inducible nitric oxide synthase (iNOS) expression.

Materials and methods. RAW 264.7 and AMJ2-C11 murine macrophages were exposed for 24 h to either IFN-γ or live IAV (A/PR/8/34), or their combination. At 24 h postexposure, cell viability was evaluated by trypan blue dye exclusion, nitrite levels in macrophage culture supernatants were measured using Griess reagent, and cells were harvested for iNOS mRNA detection by reverse transcriptase (RT)-PCR.

Results. The added IFN-γ was associated with reduced viability of both cell lines only when infected with IAV, which was coincident with an elevated level of nitrite and iNOS mRNA. Furthermore, the increase of NO generation was significantly more when IFN-γ and IAV were not used together (p < 0.05).

Conclusions. Our results indicate that IFN-γ enhances cytotoxicity in the IAV-infected macrophages by increasing expression of iNOS gene and production of NO. These findings are important for understanding the mechanism by which IAV causes injury to cells and tissues in lungs.

Keywords: interferon-gamma, influenza virus, cytotoxicity, inducible nitric oxide synthase, nitric oxide, macrophages